Ore reduction process



April 17, 1956 E. R. GILLILAND ORE REDUCTION PROCESS Filed March 5, 1952Qanudmou ZONE l at .relativelylhigh temperatures. heat required by thesereactions and to'maintain tem- ORE REDUCTION PROCESS Edwin R.Gilliland,` Arlington, Mass., assigner to Esso Research and EngineeringCompany, a corporation of VDelaware Application March 5, 1952, SerialNo. 274,874

5 Claims. (Cl. 75-26) The present invention relates to an improved orereduction process. More specifically the invention is con- ,cerned withthe production of metals of the iron type the like.

v Heretofore manyefforts have been made to utilize gaseousvhydrocarbons, particularly natural gas, as a reducing agent for the-recovery of metals from their oxidic ores, for example, recovery ofiron from iron oxide ores. Natural gas is an abundant and inexpensiveraw material.` However, its direct' use as a reducing agent for metallicores such as oxidic ores have encountered serious difficulties whichmake processes of this type unattractive in commercial operations l l JjProbably the'most important single reason for this sit'- uation must befound inf the particularly poor thermal characteristics of ordinaryhydrocarbons as'theredu'cing agent for oxidic iron ore or the like. Theprevailing rei ductionreactions involving such hydrocarbons are strong#1y endothermic and their rates become appreciable only lIn order tosupply the peratures of this high level in the reduction zone, bypreheating leither the gas feed or the ore or both, prohibitively highpreheating temperatures are required. If this heat is to be suppliedVfrom an external source through thewalls of the reduction zone,temperature and the temperature gradients are undesirably high, makingit difficult to supply heat in this manner. If it is attempted togenerate the heat within the reduction `zone itself by a combustion offuels, the reactions must be carefully con-y i United States Patent r jl 1C@ is excessive.` Far more heat may be produced by burning methaneall the way to CO2 and H20. However, as shown above, only a limited CO2concentration may be tolerated in the reductionzone, if reoxidation oflmetal is to be avoided. It is extremely dicult, therefore, to'reconcile the requirements of eicient heat generation' of solid metaloxides of the iron type with hydrocarbon gases such as methane, naturalgas or its equivalents. Other objects and advantages of the inventionwill appear from the following detailed description read with referenceto the accompanying drawing.

In accordance with the present invention these objects are accomplishedby burning a hydrocarbon gas with air in a heating zone in the presenceof finely divided iron ore (substantially Fe2`03) `maintained in a densesuspension by means of upflowing gases and their combustion products.'Combustion of the'hydrocarbon gas is carried out to an extentf that thefinely divided ore is partially reduced to an intermediate oxide andheatedto `a ternperature above thatnecessary to obtain practical ratesof reduction to metal ,in apsecond zone by a gas intro-` duced .theretooriginally as a hydrocarbon, e. g. methanel- However, the combustion iscontrolled so that the gases 4 are substantially non-oxidizing withrespect tothe 'intermediate oxide of reduced oxygen content, forexample,

, FeG. 'About v11/2 `to 2 mols of hydrocarbon `(on a methane tion zone.

' basis) are'i employed per molof Fe203 fed to the conforts-1VThe-heated partially reduced oxide is transferred by` means of anoverflow Vstandpipe from the heating zone to` a lower' reductionzonewhere it is then contactedin a dense phase suspension withundilutedhydrocarbon gas,

e. g. methane, introduced at`the bottom'of the zone. In

the reduction zone, a Vportion of the intermediate "oxide is reduced tometal and the formation of some carbon occurs due to cracking-of thehydrocarbon entering the v zone- This carbonV is` ultimately recoveredeither in the trolled so that the ratio of CO2:CO in the gas phase staysbelow the equilibrium value, at-the temperature employed, of theoxidation,` reduction reactions 'of iron oxides 'in the presence ofcarbon oxides. When employing the ore in powdered form particularly whenusing the Yso-called fluid solids technique, high temperatures `aboveabout 95057 C. in the 'reduction zone must be avoided because such hightemperatures have been found to be conducive to agglomeration ofparticles, probably as aresult of plasticization ofthe solids,particularly the reduced iron itself.Y It follows that theprocess'requires the supply of alarge amount of heat and simultaneouslya careful control of ,temperature Within relatively narrowflimits It`hasbeen suggested to supply the heat required in thezreduction' zone bythe combustion 'of substantially purehydrogen in contact with theore,-HoWeve`r,.pure hydrogen is expensive and its high costetectsadversely the economics'ofthis `type of operation. When'attemptingto2-generate sufficient heat bya partial .combustion of methane incontactwith `the ore and/or reduced metal, other'considerablediiiiculties arise. In `the iirst` place the oxidation of methane merelytoCO` has only a rather insignificant positive heat effect `so that whensubstantial amounts of heat are required the methane consumption metalproduced, or else it finds its way into'thegasilica-V v tion zone,between the reduction zone and the heating zone. Carbon in the productis desirable, for example,

. in the production of pig iron, since a few .percent of carbon lowerslthe melting point of, theV irons'everal hundred degrees.` If carbon ispresent and is considered'undesirable, the Vbottomsproduct from thereduction zone should contain a` small amount of unreduced oxide mixedwith the metal, such that von subsequentsoaking of the hot Withdrawnproduct the oxide would just consume the amount of contained carbon. Thereductiony zone functions as a buoyancy separator to' separate metalfrom thev partially reduced intermediate oxidefwith `the result that theoxide `forms an upper lighter phase and is'carried back into the heatingzone" 1 ywith the aid of the highvelocity-airgor othercombustion-supporting gas entering the base of the heating zone viarline 4. tIn order to supply the required heat `to the reduction zoneitis necessary to circulate theretoY from the heating zone approximately1010.20 volumes of intermediate oxide for each volume of oxide reducedto metal in thereductionzone.

l The ore in kthe heating zone is brought up toa,tempera ture intheneighborhood. of ,about 1000"` ClZOO` C. in

the *Casar-'Off .PHONl A? femparatilrtfin f this rgion, -pf

course, care should be exercised t`o maintain the com- 2,742,352 lPatented .Abr-,17, 1,95

' @Blasts hydrssarb apparent from the. folio ing descriptionwhenl reaQOnHsCtQIl-Witltthsdrullisfuhishfisassmrdlssfsmrssti' ssl illustraties fthe aptzaratus suitablsfsrfths.; mastic@ of the invention.

, Referring. to the drawing the` apparatus consists essentially of aheating and partial reduction zone 1; equipped with air sorts4.ansl-0lefssslflgli1ss 6.sas removal 8 and. sslld.- removal; means;Ain.. the tous of. an oserew standpipe 3. Beneath the heatingfzo'ne islareduction zone.

2. communicates with the heating zene Tfhs. reduetion Qns-Cantal@sas-reus fsrths. inttsdsstisnot undilutedhydrsalbanfsasssltatis..sasssssmainss no appresa.-

bls.- amsunts sf ssslbustisnfsurpe., .ne eases sich. as. sir Qn Qsvesn-Baisses-.Ore presses (metal.)` is rsmevedrsm the bQttOm-sf thsrsdustignloteria. withdrawal, line 1Q.

2911s. 1f Pretfably has-a lasser horizontal; cross. sectional;

arse-than Zeus Tf dus te the. nsssssity. fet handling. the

lar-ssn YQlums Ot sas. in` the;` form. of; hydrocarbon, air and.

combustion products in zone In theoperation of the apparatus oli the drawingbnelydivided iron` orev c ont-ainingiron in a, high stateofs'oxidation and havingy a iiuidizable particle size distributionbetut/.611.50 microns and 20,mesh is Supplied to zone 1 Via.

lines 61f In this zone(` the oreis preheated and partially re.- dupedbyhot combustion. gases, as willappar more clearly hereinafter, toltatemperature as highi as about 120()` C. in. the. caserof EezOa. I n zone-.1 the iinelydivided solid; is. kept inA a highly agitated dense,suspension, by proper main.- 'lslllls 0f vslpsitssof: sasesentering thezone 1. via. lines.A

4L and. frQmf zons.- 2.2 The solid. is: maintained. at a level L abovewell r1 1 of standpipe suchA that thehot. solid oven.. llQWS. into. illsstandnins and isallowedjto descend therein. toreductiron zone. 2- vIn:reduction zone 2 the hot solid. gas, such as methane or. natural.

In: zone 2. s

gasrsstsrins the .bottom thereof via 'line 5A, the solids are maintainedin the form of a dense .turbulent suspension; by means oh hydrocarbon.gases. entering through line Sand; Oxidation. products of such gasesOnes reaction of these` gases withthe hot. oxide occurs. The hydrocarbongas,entering. line.5v is undiluted, that. i s, conf. tainssubstantiallyno airoxygen, or other gasesijoxidiz: ing4 with-respect to iron metal,In zone. 2- the. solidy is.

s converted by the upwardly owinghydrocarbon. gas. (and` For this.

4 solids are removed in the cyclone system and returned to los?. 1. via.sigles.. 9 is. recovered.. trans. the. dus. gases in exit pipev 8 byconventional means.

All the hydrocarbon gas supplied to the system is introduced thereto Vialines 5. However, it may sometimes be desirable to introduce a portionof such gas directly to zone l since this reduces the amount oflheatrequired to be carried from zone 1 to zone 2; it is understood,however, that the amount Qffhydrcatlssusas admitted@ the reduction zone2 cannot be reduced below that required for reduction oftheoxidetometal.,

The hydrocarbon gas employed in the reduction zone is preferablypreheated to a temperature below its cracking temperature, sayabout300.t0 5.009 C. Its amount is so controlled that suficient. hydrocarbonAis present for the reduction of the iron oxide and for supplying thenecessary heat for reduction in zone 2. Compressed air entering throughline 4 is preferably preheated to a temperature of; about SSW-209 G.preferably-in heat exchange with hotI com bastion` gases. removed! from.the` system via. line 8.` 'Ehetotal amount of air. ledV through line4.-is. soA controlled that just enoughI oxygen is made available in theheatingl Zone to. maintain therein in eooperationwithz any oitygen` of.the solidi an average` temperature above. the temperature 0f. Zone1 l'but not in. appreciable.v excess of 1200"' C. About 2-to 4 normal cu.ft. of air per. cu. ft. ofr methanev suppliedyto reductiony chamber 2.is sufficient for good operating conditions. It should be borne ins mindthatv the amount of air. should be such and introf A atsuch. a ratethat. willi leave the gas in zone 1 still non-oxidizing in characterto.V FeQ. Thus, in. a. satis.- f actoryoperation, the vratio.offCOz-Iewater vapor/ @Oft-Hz in,l the` gases leaving. zone 1 will. begreaten than 2:15. It. iS 3.- lIlQWIl aQt. that; the. air introducedthrough. line 4; will rise vertically with almost no back downward flow.The combustion. of thilsiairlwith. the hydrocarbonv and' its Vip aetiouprfduct; emerging from. zone 2 and enteringthe bottoni of zone Lgeneratesall theheat. necessaryforthe.

- endothermi reduction. reaction occurring in zone. 2'. The

applied. Hpwsvsrsthe solids shouldamount to atleast.

5% and preferably more than .10%l by volumeof the dssssnlissa Y Y 111the redutisn 2011s apnroximately 1.0- to 2.0 volume resilient-'0fthssirsulatins ir-onoxids isrsdusetl to metallic iron. which separatesoutl ofthev fluid bed due to. change in density. This separated ironcollects in a.pool..12 at the bottom of zone.2. Metal: is drained. oif`fromzone 2 via pipe 10 which is equipped with a ceramic plugy typevalve. 1

Gases emerging from reduction zone Z-p'ass upwardly into zone 1-. Inzonel combustion of thesegases, SHA1,

previously rela-ted;y Combustion gases are--removedefrom the heatingone'via cyclone *7A and exiftpipe -8. Entrained M. n.. sa,

flownflQW Of the. hotsolidsviastandpipe 3..ser.ves to .trans port thatheat. toreductionzone 2, the hot oxide entering the reduetionzoneaty apoint below the. point of air. ad.- missionl to zone 1. Itis inthereduction zone. that sub. stantially all; the. actual; reduction offthe. oxide tometal' takes place. Aspreviously. explained; the heatingvessel; has a topI horizontal'. cross.A section which is large.,relative. t9 tllmsseetion Off YesselzZbecause .inthe top one must'.proyide fon the large extra volume ofrgas brought in.. as air.

Beducediron Ore in the form ofsponge ironl andy con.- taining controlledgamounts. of carbonis withdrawnthrough4 draw-ofte linelibandpassed toa meltingfurnace suitable. to the processing of:powdered-xspongeiron. of.- the type hsreinvolyed,

Having. described: the. invention. in a. manner.- such that( it may'v bepracticed; by. those. skilled'. inA the. art, what isl Qlaimedis.: s

1. `ProcessI for'reducing I netal oxides of the irontype, saidl oxidesexisting inz theforrn. oi a higher.- oxdeand a lower. oxide, whichcomprises supplying timely dividedhigher metal; oxide. .toA a first.heating. anda partial reduction zone, supplying ay gaseous.vhydrocarbon-containing. fuelA mixed-with lower metal.y oxide. from asecondreduction zone to saidl rstheatingv zone,v admixingcombustion-sun. porting. gas with. said gaseousfueLasit is passed..from. said secondreduction zone tosaidrstheatingzrone, maintainf ing themetaloxides influidized statein saidrstlheating zone, burning. thefuelwith the combustion-supporting gas in the presence-othemetaloxideswhereby thehigher metaloxide -is reduced to a'lower metal oxideand sensible heat -isimpar-:ted thereto, removing fluidizedj hot lowermetal-oxide from saidsrst heatingand partialreducption zone directly tothe second reduction zones supplying to saidfsecond reduction zonegaseous hydrocarbon substantially -frpee of combustion-supporting gas toreduce the t trolling the velocity of gases passed through said secondreduction zone so that the solid contents therein are maintained in afiuidized metal oxide base and a separated metal phase, removing astream of the metal vfrom said second reduction zone, and returningunreduced lower metal oxide from the second reduction zone mixed withhydrocarbon-containing fuel gas from said second reduction zone to saidfirst heating zone.

2. The process for reducing metal oxides of the ironv type, said oxidesexisting in the'form of a higher oxide and a lower oxide, whichcomprises supplying the finely divided metal oxide to a first heatingand partial reduction zone, supplying gaeous hydrocarbon-containing fuelto said heating zone, admixing combustion-supporting gas with saidgaseous fuel asit is passed into said heating zone, maintaining metaloxides in a fluidized state in said `heating zone and` partial reductionzone, burning the gaseous fuel with the adrnixed combustion-supportinggas to reduce the higher oxide to the lower oxide and impart sensibleheat thereto, removing combustion gases from said first heating andpartial reduction zone, removing fluidized hot` lower metal oxide fromthe first Y heating and partial reduction zone to a second reductionzone, introducing into said second reduction zone gaseous hydrocarbon,reacting a portionof the hot lower metal gaseous fuel therefor, removinga stream of said separated metal from said reduction zone, and returningunreduced lower metal oxide from the second reduction zone to said firstheating zone. Y Y

3. The process defined in claim 2 in which the higher oxide is FezOzwhich is converted to the lower oxide FeO in the first heating andpartial reduction zone, the lower metal oxide is converted to metallicFe in the second reduction zone, and in which natural gas is the gaseoushydrocarbon introduced vinto said reduction zone and subsequently mixedwith air as said combustionsupporting gas in passing from the secondreduction zone into said first heating zone.

1 4.` The process as defined in claim 2, in which the lower' metal oxideis heated to a temperature in the range of 1000 to 1200 C. in said firstheating and partial reduction zone and in which a temperature of 750 to950 C. is maintained in the second reduction zonet to convert 10 to 20volume percent of FeO as the lower metal oxide into the Fe metal in saidreduction zone.

5. The` process for reducing iron oxides, which comprises supplyingfinely divided `FeaOa to a first heating and partialreduction zone,supplying a natural gas hydrocarbon-containing fuel to said firstheating zone, introducing oxygen-containing gas and supporting combus'tion gases into said heating zone, maintaining iron oxides in afiuidized state in said heating and partial reduction zone, burning thefuel in said introduced oxygen-containing gas as the gases are passed upthrough said zone in the presence of the finely divided ferrie oxide toreduce the FezOsl particles to FeO particles and impart sensible heatthereto, removing combustion gases overhead `from said zones, removingfiuidized hot FeO particles from said partial reduction zone to a secondreduction zone,

reacting a portion of the hot FeO in the second reduction zone with gasoriginally introduced thereto as a natural gas hydrocarbon andsubstantially free of combustion supporting gas to reduce the FeO tometallic Fe,'con trolling the velocity of gases passed upwardly throughsaid second reduction zone so that solid contents thereof are maintainedin a fluidized FeO phase and a separated metallic Fe phase, introducingthe resulting gaseous stream comprising excess hydrocarbon, C0 and H2with uidized FeO from the upper part of said second reduction zonedirectly up into a bottom part of said first heating zone to supply saidfuel therefor and to reheat the FeO in said heating zone, removing thestream of the metallic Fe from said secondreduction zone, and returningunreduced hot FeO with the FeO formed by the FezOa from said firstheating and partial reduction zone as a relatively confined streamdownwardly into said second reduction zone.

References Cited in the le of Vthis patent UNITED STATES PATENTSOgorzaly July 10,` 1951

1. PROCESS FOR REDUCING METAL OXIDES OF THE IRON TYPE, SAID OXIDESEXISTING IN THE FORM OF A HIGHER OXIDE AND A LOWER OXIDE, WHICHCOMPRISES SUPPLYING FINELY DIVIDED HIGHER METAL OXIDE TO A FIRST HEATINGAND PARTIAL REDUCTION ZONE, SUPPLYING A GASEOUS HYDROCARBON-CONTAININGFUEL MIXED WITH LOWER METAL OXIDE FROM A SECOND REDUCTION ZONE OF SAIDFIRST HEATING ZONE, ADMIXING COMBUSTION-SUPPORTING GAS WITH SAID GASEOUSFUEL AS IT IS PASSED FROM SAID SECOND REDUCTION ZONE TO SAID FIRSTHEATING ZONE, MAINTAINING THE METAL OXIDES IN FLUIDIZED STATE IN SAIDFIRST HEATING ZONE, BURNING THE FUEL WITH THE COMBUSTION-SUPPORTING GASIN THE PRESENCE OF THE METAL OXIDES WHEREBY THE HIGHER METAL OXIDE ISREDUCED TO A LOWER METAL OXIDE AND SENSIBLE HEAT IS IMPARTED THERETO,REMOVING FLUIDIZED HOT LOWER METAL OXIDE FROM SAID FIRST HEATING ANDPARTIAL REDUCTION ZONE DIRECTLY TO THE SECOND REDUCTION ZONE, SUPPLYINGTO SAID SECOND REDUCTION ZONE GASEOUS HYDROCARBON SUBSTANTIALLY FREE OFCOMBUSTION-SUPPORTING GAS TO REDUCE THE LOWER OXIDE TO METAL IN SAIDSECOND REDUCTION ZONE, CONTROLLING THE VELOCITY OF GASES PASSED THROUGHSAID SECOND REDUCTION ZONE SO THAT THE SOLID CONTENTS THEREIN AREMAINTAINED IN A FLUIDIZED METAL OXIDE BASE AND A SEPARATED METAL PHASE,REMOVING A STREAM OF THE METAL FROM SAID SECOND REDUCTION ZONE, ANDRETURNING UNREDUCED LOWER METAL OXIDE FROM THE SECOND REDUCTION ZONEMIXED WITH HYDROCARBON-CONTAINING FUEL GAS FROM SAID SECOND REDUCTIONZONE TO SAID FIRST HEATING ZONE.